The present invention relates generally to integrated circuit (IC) packages and more specifically to lead frames for use in an integrated circuit package and methods of forming the lead frame.
In the IC packaging industry, there is continuous pressure to reduce the cost of packaging ICs. To accomplish this, a wide variety of package designs and assembly methods have been developed. One of the major concerns when designing integrated circuit packages is dealing with the heat generated by the integrated circuit die during its operation. The amount of heat generated by the die varies dramatically depending on the specific die used in the package. Therefore, in order to minimize the cost of producing a given integrated circuit package, the heat dissipating characteristics of the integrated circuit package should be designed to be sufficient to deal with the heat generated by the die of the package without adding any unnecessary cost to producing the package.
In a conventional IC package, the majority of the heat generated by the die is dissipated through the leads of the package. This is because the leads provide the best thermal path away from the die and the die attach pad on which the die is typically supported. Currently, in a situation in which the die generates more heat than can be properly dissipated through the leads of a conventional integrated circuit package, a heat slug or other such heat dissipating device is included in the package to improve the heat dissipating characteristics of the package. The die typically attached directly to the heat slug and one surface of the heat slug is left exposed when the package is encapsulated thereby providing a direct thermal path from the die out of the package. In an example, a package including a heat slug may have a thermal dissipating capacity one hundred times that of a conventional package without a heat slug. Although this approach substantially improves the heat dissipating characteristics of the package, it also increases the cost of the package. In many cases, this approach of adding a heat slug provides much more heat dissipating capability than is necessary and therefore unnecessarily increases the cost of the package. For this reason, it is desirable to provide a package that improves the heat dissipating characteristics of the package without adding all of the costs associated with providing a heat slug.
FIG. 1 illustrates one prior art approach to improving the heat dissipating characteristics of a package without adding a heat slug. This approach is referred to as the thermal coastline approach. In the thermal coastline approach, the die is supported on a die attach pad of a lead frame. The die attach pad and the leads are configured to increase the area of the ends of the leads which face the die attach pad in order to increase the thermal transfer from the die attach pad to the leads.
FIG. 1 is a partial diagrammatic plan view of a lead frame 10 using the thermal coastline approach. Lead frame 10 includes a die attach pad 12 and a plurality of leads 14 for electrically connecting a die (not shown) to other external elements. As illustrated in FIG. 1, leads 14 and die attach pad 12 are formed such that their edges, indicated by edges 16 and 18 respectively, face one another along a line that is at an angle A relative to the symmetrical axes of the lead frame indicated by center lines 20 and 22. When comparing this configuration to a conventional configuration, this angling of the edge surfaces of die attach pad 12 and the facing leads 14 increases the surface area of each of the edges 16 of the leads 14 that face edge 18 of die attach pad 12.
Since the amount of the surface area of the leads facing the die attach pad significantly impacts the heat dissipating characteristics of the lead frame, the above described configuration improves the heat dissipating characteristics of a package using this type of lead frame. However, this approach is limited by the amount that the surface area of the facing edges may be increased without creating other problems such as increasing the size of the package. Generally, the thermal coastline approach may provide an improvement of up to about 20 percent in the heat dissipating characteristics of a given package compared to a conventionally configured package that uses a lead frame with a square edged die attach pad and leads.
Accordingly, it is desirable to provide a package configuration having even greater thermal dissipating characteristics than the above described thermal coastline approach without requiring the use of a heat slug or any other such additional heat dissipating device. The present invention provides arrangements and methods of producing lead frames and integrated circuit packages which are capable of substantially improved heat dissipating characteristics compared with conventional packages that do not include a heat slug or any other additional heat dissipating device. The present invention accomplishes these improved heat dissipation characteristics without requiring the use of a heat slug or any other additional heat dissipating device.